Polycrystalline oxide channels have the properties of high mobility, resistance to acid etching, excellent stability and the like, and the manufacturing techniques thereof are highly concerned in the display panel industry.
Crystal growth takes place in two manners, i.e., homogeneous growth, and heterogeneous growth. The homogeneous growth requires a high degree of undercooling, and it is relatively difficult to grow a crystal in this manner. The heterogeneous growth takes place with the aid of foreign particles or existing nuclei. As less energy is required, the heterogeneous growth takes place quickly. Moreover, according to the theory of crystal growth, atoms are less prone to pack on a smooth interface, in which case crystal growth takes place slowly. In contrast, atoms are liable to pack on a coarse interface, in which case crystal growth takes place quickly.
In2O3, ZnO, Ga2O3, SnO2 and composites thereof which are used in the current oxide channels have an extremely high melting point (above 1000° C.) and crystallization point respectively, the processes of film forming of polycrystalline oxide channels generally take place at a faster film forming rate, and the substrates for film forming are mostly in amorphous state. Therefore, the oxide thin films formed by conventional processes, e.g., magnetron sputtering deposition, pulsed laser deposition, and solution process for preparation of amorphous film, are generally in amorphous state. High energy is required to convert such amorphous thin films into polycrystalline state, for example, by ultra-high temperature annealing (greater than 450° C., usually about 600° C.), which will consume much energy.
In the existing production line of TFT array substrates, the annealing equipment typically has an upper temperature limit of 450° C. When the temperature exceeds 450° C., the annealing equipment will face great challenges in the heater and the homogeneity of heating. Consequently, it is relatively difficult to perform the ultra-high temperature heat treatment on the production line after film forming. Moreover, the high temperature annealing treatment has drawbacks including high requirement on the performance of the glass substrate, high energy consumption and the like.
Therefore, development of a process for manufacturing a TFT array substrate having polycrystalline oxide channels on the existing production line has become the focus of research.